You Don’t Need a Weatherman to Know Which Way the Wind Blows: Delaying Spectrum Auctions

The leaders of the House science committee – both the chair and the ranking member – sent a very peculiar letter to the FCC seeking to delay the auction of microwave spectrum for 5G. The letter is peculiar because it addresses an issue that has already been examined by multiple government agencies and settled.

The issue is whether 5G operation in the 24 GHz band will disrupt weather satellites operated by NOAA and NASA that use spectrum in the adjacent 23.8 GHz band. Press accounts of the issue also mention concerns about weather data gathering platforms that use lower frequencies – 1.675 to 1.695 GHz – but these are not parts of the auction.

The letter goes back to the 1970s to document controversy about weather data systems, and relies heavily on issues raised a decade or more ago. The relevance of these asides is, frankly, a bit mystifying.

 The Frequencies Don’t Overlap

The FCC proposes to auction 6 100 MHz blocks of microwave spectrum ranging from 24.25 to 25.25 GHz. The lower edge of this allocation is 425 MHz above the upper limit of the band used by microwave vapor sensors.

The letter addresses worries that land-based 5G fixed and mobile licenses will interfere with space-to-earth transmissions between polar satellites and two ground stations, one on Fairbanks, Alaska and the other in France. These satellites also sense microwave energy radiated by the oceans, but that wouldn’t be much of an issue given that the licenses only cover the US land mass.

Based on nothing more than speculation about possible harm, NASA and NOAA raised the issue in a group of government stakeholders, where it was decided by the State Department acting as a neutral arbiter. Given the high directionality of microwave signals and the difference in the applications, the resolution is completely unsurprising.

Microwave is the M in “MCI”

Most of the land-based microwave used in the US is used for backhaul, from one fixed location antenna to another. This has been the case since the early days of MCI, the microwave-based telephone carrier that helped end the Bell System monopoly on long distance calling.

Microwave is great for backhaul because its signals can be tightly focused. This ends the problem of signal degradation over distance (“free space path loss”) and eliminates most forms of interference.

Microwave signals can criss-cross each other in dense deployments without interfering. It’s essentially the equivalent of a wire in most settings. Hence, the fear that a land-based microwave network will interfere with a space-based system is not well grounded.

Noise Threshold Rears its Head Again

Whenever a hidebound incumbent wishes to prevent the rise of an innovative entrant that uses RF spectrum, the noise floor rears its ugly head. This was the case when the FCC proposed to allow pulsed Ultra-Wideband waveforms to overlay incumbent mobile phone systems as well as when carriers explored the use of unlicensed bands for LTE.

This claim is like the “toxic cloud” argument used by crafty toxic tort lawyers to win settlements from gullible juries against factories that use a number of chemicals within allowed thresholds. Although plaintiffs can’t identify actual violations, they argue that some combination of non-harmful emissions adds up to something horrible.

In this case, the complainers seek to protect incumbent systems from the remotest possibility of harm by constraining terrestrial microwave to a ridiculously low noise threshold. The FCC set the noise threshold in adjacent bands at -20 dBW, a perfectly reasonable level. The science committee letter insists on a tiny fraction of this level, below -50.

Ridiculous Demand

This is a ridiculous demand. Satellite-based weather sensors are very low bandwidth systems; many operate at data rates between 100 and 1200 bits per second.

Signals carrying so little data are inherently immune to most kinds of interference, and their response times range from minutes to hours. This is not sensitive data that can be easily harmed by interference.

Satellite-based systems are also vertical on nature, while 5G is a horizontal, land-based system. So it appears that a political constituency has asked for an unnecessary delay in order to protect itself from the consequences of 5G.

It’s a whole lot better for these firms to embrace 5G and make it part of their business plans than to seek to delay it. 5G is a radical redesign of the cellular network that offers more to consumers than does a continuation of the status quo.